title: Flagellum elongation is required for correct structure, orientation and function of the flagellar pocket in Trypanosoma brucei.
abstract: In trypanosomes, the flagellum is rooted in the flagellar pocket, a surface micro-domain that is the sole site for endocytosis and exocytosis. By analysis of anterograde or retrograde intraflagellar transport in IFT88RNAi or IFT140RNAi mutant cells, we show that elongation of the new flagellum is not required for flagellar pocket formation but is essential for its organisation, orientation and function. Transmission electron microscopy revealed that the flagellar pocket exhibited a modified shape (smaller, distorted and/or deeper) in cells with abnormally short or no flagella. Scanning electron microscopy analysis of intact and detergent-extracted cells demonstrated that the orientation of the flagellar pocket collar was more variable in trypanosomes with short flagella. The structural protein BILBO1 was present but its localisation and abundance was altered. The membrane flagellar pocket protein CRAM leaked out of the pocket and reached the short flagella. CRAM also accumulated in intracellular compartments, indicating defects in routing of resident flagellar pocket proteins. Perturbations of vesicular trafficking were obvious; vesicles were observed in the lumen of the flagellar pocket or in the short flagella, and fluid-phase endocytosis was drastically diminished in non-flagellated cells. We propose a model to explain the role of flagellum elongation in correct flagellar pocket organisation and function.
authors.affiliation: Trypanosome Cell Biology Unit, Pasteur Institute and CNRS, 25 rue du Docteur Roux, 75015 Paris, France.
authors.forename: Sabrina
authors.initials: S
authors.lastname: Absalon
authors.forename: Thierry
authors.initials: T
authors.lastname: Blisnick
authors.forename: Mélanie
authors.initials: M
authors.lastname: Bonhivers
authors.forename: Linda
authors.initials: L
authors.lastname: Kohl
authors.forename: Nadège
authors.initials: N
authors.lastname: Cayet
authors.forename: Géraldine
authors.initials: G
authors.lastname: Toutirais
authors.forename: Johanna
authors.initials: J
authors.lastname: Buisson
authors.forename: Derrick
authors.initials: D
authors.lastname: Robinson
authors.forename: Philippe
authors.initials: P
authors.lastname: Bastin
mesh_terms: D000818:Animals; D004705:Endocytosis; D005407:Flagella / Q000737:chemistry* / Q000235:genetics / Q000502:physiology* / Q000648:ultrastructure; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D015800:Protozoan Proteins / Q000235:genetics / Q000378:metabolism; D014346:Trypanosoma brucei brucei / Q000737:chemistry* / Q000235:genetics / Q000502:physiology* / Q000648:ultrastructure
chemical_list: D008565:Membrane Proteins; D015800:Protozoan Proteins; C065453:cysteine-rich, acidic integral membrane protein, Trypanosoma brucei